Valves of this type are encountered, for example but not exclusively, in micropumps for medical use which deliver a regular and controlled quantity of medication. The manufacture of micropumps is based on the technologies of micro-machining silicon and of using a piezo-electric actuator. International patent application PCT IB 95/00028 describes a self-priming micropump. In that application, as in others, it is necessary to make an inlet valve and sometimes an outlet valve so that the leakage rate is minimized or even zero. The leakage rate from a valve corresponds to the rate at which liquid flows through the valve when the membrane is in its rest position, i.e. when the valve is closed. Furthermore, since the valve operates because of the elasticity of the membrane, with this elasticity allowing the membrane to deform when fluid is injected to the inlet of the valve at sufficient pressure, it is important not to degrade the mass and surface state of the membrane when manufacturing the valve in order to obtain a membrane that presents a minimum amount of internal stress.
The object of the present invention is to provide a machined liquid inlet/outlet device having a minimum leakage rate in the closed position of the valve and in which the method of manufacture leads to a membrane having good physical and mechanical properties with little internal stress.
When the problem arises of covering a substrate with a thin metal layer, various methods can be used. The thin metal layer can be deposited on the substrate by evaporation, or by the cathode sputtering technique. Nevertheless, those methods have certain limitations.
Usually, metal layers that have been deposited have physical properties that are less good than those of the same materials in solid form. Thus, the layer is usually obtained with considerable amounts of internal stress, particularly because of the crystal structure of the deposited layer which is very sensitive to deposition conditions. Furthermore, a deposited thin layer is of a thickness that is limited to about 1 micrometer, since greater thicknesses cause the method to become too expensive because the time required to make the deposit is too long.
Another possibility consists in depositing the metal layer electrolytically, which technique does not suffer from all of the above-mentioned drawbacks. Nevertheless, it is not possible to deposit all materials, and in particular metals, by that method, and the physical and mechanical properties of the deposited layer are often insufficient.